diff --git a/.env.standalone b/.env.standalone
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+# Standalone build: no backend services configured.
+#
+# Used for any deploy where this app is served as plain static files and cannot
+# reach our signaling server — an itch.io upload, a subpath host, a fork without
+# a server of its own. Build with:
+#
+#   npx vite build --mode standalone --base=./
+#
+# Multiplayer is gated on this being falsy (`main.ts`'s
+# MULTIPLAYER_SERVER_CONFIGURED); `updateMultiplayerTabEnabled` then hides the
+# tab entirely, so the build never advertises a mode it cannot connect.
+#
+# This file states intent in one greppable place. It is not a guarantee — Vite's precedence means a .env.standalone.local silently overrides it (measured: the Multiplayer tab came back). Only checking the built artifact holds.
+VITE_MULTIPLAYER_SERVER_URL=